Axon degeneration occurs in a variety of neurodegenerative diseases such as Parkinson's and Alzheimer's diseases as well as upon traumatic, toxic or ischemic injury to neurons. Such diseases and conditions are associated with axonopathies including axonal dysfunction. One example of axonopathy is Wallerian degeneration (Waller, Philos Trans R. soc. Land 140:423-429, 1850), which occurs when the distal portion of the axon is severed from the cell body. The severed axon rapidly succumbs to degeneration. Axonopathy can, therefore, be a critical feature of neuropathic diseases and conditions and axonal deficits can be an important component of the patient's disability.